Dosage forms made in the form of an osmotic delivery system are known to the delivery art in U.S. Pat. Nos. 3,845,770 and 3,916,899, both issued to patentees Felix Theeuwes and Takeru Higuchi. The dosage form disclosed and claimed in these patents comprise a semipermeable wall that surrounds a compartment containing a beneficial agent, usually a beneficial drug.
The wall is permeable to the passage of an external fluid and substantially impermeable to the passage of a beneficial drug. There is at least one passageway through the wall for delivering the beneficial agent from the dosage form. The dosage form releases the beneficial agent by fluid being continuously imbibed through the wall into the dosage form at a rate determined by the permeability of the semipermeable wall and the osmotic pressure gradient across the wall. This physical-chemical action produces a solution containing the beneficial agent that is hydrodynamically dispensed through the passageway from the dosage form.
The above described patents also are useful for delivering a beneficial agent that exhibits a low solubility, or exhibits a high solubility in an external fluid imbibed into the dosage form. The dosage form delivers such beneficial agent by blending the beneficial agent with an osmotically--effective solute, known also as osmagent. The osmagent in the dosage form are a substantial motive force as they exhibit an osmotic pressure gradient across the wall of the dosage form, and they imbibe fluid into the dosage form. The osmagent produces a solution with the imbibed fluid that is osmotically delivered from the dosage form concomitantly transporting therewith undissolved, or dissolved beneficial agent form the dosage form.
The dosage form of these patents is an outstanding invention and its represents a pioneer advancement in the delivery art, and it is endowed with ideal delivery kinetics useful for delivering these beneficial agents. Now, it has unexpectedly been discovered there is an occasional instance where the delivery kinetics of the dosage form can be improved leading to even more desirable results. For example, when a beneficial agent exhibits a low or a high solubility and is mixed with an osmagent to produce an equilibrium ratio, the resulting beneficial agent solubility in the presence of all of the osmagent often is too small, usually less than 50 mg/ml, or to high, usually greater than 400 mg/ml, for rendering this blend dispensable at a controlled rate over a prolonged period of time. When the resulting beneficial agent's solubility is low, it is difficult to deliver the beneficial agent at meaningful therapeutic rates; and, when the resulting beneficial agent's solubility is to high it is delivered from the dosage form in a premature period of time.
Thus, in the light of the above discussion, it will be readily appreciated by those versed in the subject art that a critical need exists for a dosage form for delivering a beneficial agent that exhibits a hard to delivery solubility, especially where the dosage form overcomes the tribulations associated with the prior art. Likewise, it will be further appreciated by those skilled in the art, that if a novel and useful dosage form is made available for delivering these beneficial agents, such a dosage form have a positive value and also represent a substantial contribution to the dispensing art.